EP1092261A1 - A continuous mode flyback converter - Google Patents

A continuous mode flyback converter

Info

Publication number
EP1092261A1
EP1092261A1 EP99948572A EP99948572A EP1092261A1 EP 1092261 A1 EP1092261 A1 EP 1092261A1 EP 99948572 A EP99948572 A EP 99948572A EP 99948572 A EP99948572 A EP 99948572A EP 1092261 A1 EP1092261 A1 EP 1092261A1
Authority
EP
European Patent Office
Prior art keywords
converter
secondary side
fet transistor
transistor
continuous mode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99948572A
Other languages
German (de)
French (fr)
Inventor
Claes SVÄRDSJÖ
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telefonaktiebolaget LM Ericsson AB
Original Assignee
Telefonaktiebolaget LM Ericsson AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Telefonaktiebolaget LM Ericsson AB filed Critical Telefonaktiebolaget LM Ericsson AB
Publication of EP1092261A1 publication Critical patent/EP1092261A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

  • the present invention relates to a DC-DC converter circuit, and m particular to a synchronous flyback converter circuit for operation m a continuous mode.
  • power rectifiers are utilized m order to output a correct rectified output voltage.
  • a diode would be employed on the secondary side m order to obtain the rectified output voltage .
  • flyback topology a primary side stores magnetic energy m a magnetisable core or the like during a charging interval. The energy is then fed to a secondary side during the so called flyback interval.
  • the main advantage of a power rectifier circuit having a flyback topology compared to other rectifier circuits is its simple construction, which makes it cheap to manufacture.
  • flyback converters can be divided into two different kinds:
  • m a conventional flyback converter as seen m Fig. 1, which comprises, on the primary side, a primary winding 101 of a transformer 105 and a switch 103, and on the secondary side a secondary winding 107 of the transformer 105 connected to a diode 109 and an output capacitor 111 over which a load 113 can be connected, there is a problem associated with the voltage 2
  • the voltage drop over the diode 109 becomes a significant part of the overall voltage, which makes the power converter inefficient for such low voltage applications.
  • US patent No. 5,237,606 describes a power converter to be located in a remote terminal of a telephone system.
  • the power converter is designed to be able to operate both in a continuous mode and in a discontinuous mode, which can occur in the specific application for which the power converter is designed.
  • the power converter deals with the problem of a large voltage drop over the rectifying diode on the secondary side by means of using a FET transistor.
  • the aim is to provide a power converter which can operate both in a continuous mode and in a discontinuous mode, the circuit is not well suited for use in a continuous mode. This is due to the fact that in order to work properly in the discontinuous mode, control circuits are required, which besides being expensive, also galvanically interconnects the primary and secondary side of the power converter, thereby taking away the galvanic isolation between the primary and secondary side.
  • - Fig. 1 is a circuit diagram of a continuous mode DC-DC converter according to the prior art.
  • - Fig. 2 is a circuit diagram of a continuous mode DC-DC converter having a FET transistor as rectifying component.
  • - Fig. 3 is a circuit diagram of a continuous mode DC-DC converter having a FET transistor as rectifying component and having an improved drive circuitry.
  • a DC-DC converter comprises on the primary side a primary winding 101 and a switch 103, the primary winding being supplied with power from a DC voltage source 102.
  • the DC-voltage source can m turn be connected to an AC-voltage supply (not shown) via a rectifying circuit.
  • the primary side feeds a secondary side with energy via a transformer 105.
  • the secondary side comprises a secondary winding 107 and an auxiliary winding 108 connected m series with the secondary winding 107.
  • a FET transistor 110 is with its source terminal connected to a point between the secondary winding 107 and the auxiliary winding 108.
  • the gate of the transistor 110 is directly connected to the other end of the auxiliary winding 108 and the dram of the transistor 110 is connected to one end of an output capacitor 111.
  • the other end of the output capacitor is connected to the free end of the secondary winding 107.
  • a load 113 can then be applied over the output capacitor 111, thus connected m parallel thereto.
  • the advantage of such an arrangement compared to the arrangement described above in conjunction with Fig. 1, is that the voltage drop over the diode 109 is replaced by the voltage drop over the FET transistor, which typically is much smaller. I.e. instead of a voltage drop of 0.3 - 0.7 V, which is common for most diodes a voltage drop of less than 0.1 V can be obtained, whereby the efficiency of the DC-DC flyback converter is increased, especially when the output voltage is small, e.g. less than about 5 V. Furthermore, as is obvious, the smaller the output voltage the more important the use of a rectifying component having a low voltage drop becomes .
  • a DC- blockmg capacitor 117 is inserted between the output terminal of the auxiliary winding 108 and the base of a PNP transistor 115 arranged connection to the transistor 110. Due to the collector-base diode the transistor 115, the gate voltage of the FET transistor 110 is prevented from going negative. The transistor 115 also provides a very quick turn off of the channel the FET transistor 110, so that the switch loss will be reduced to a minimum.
  • the base of the PNP transistor 115 is through the blocking capacitor 117 connected to the free output terminal of the auxiliary winding 108, the emitter of the PNP transistor 115 is connected to the gate of the FET transistor 110 and the collector of the PNP transistor 115 is connected to the source of the FET transistor 110.
  • the base and the emitter of the PNP transistor are interconnected by a resistor 119 for providing a voltage drop between the base and the emitter of the transistor 115.
  • the resistor can be replaced by a diode or another component, which can provide the voltage drop.
  • control pulses will be fed to the gate of the FET transistor 110 even m the event that the output terminals of the DC-DC power converter should be shortened. This is very advantageous since if no control pulses would be fed to the FET transistor 110 the output current should be forced to go through the body diode of the FET transistor 110. This would lead to high losses and possibly the FET transistor could be damaged .
  • topology as described above can also be applied to other types of converters, such as Cuk and SEPIC converters.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

In a continuous mode flyback converter an FET transistor (110) is provided for reducing the voltage drop at the secondary side of the transformer. The use of the FET transistor makes the converter more suitable for low voltage applications since smaller power losses are imposed in the secondary side of the converter than in a conventional converter. The converter also has a DC-blocking capacitor (117) for further reducing the power losses at the secondary side.

Description

A CONTINUOUS MODE FLYBACK CONVERTER
TECHNICAL FIELD
The present invention relates to a DC-DC converter circuit, and m particular to a synchronous flyback converter circuit for operation m a continuous mode.
BACKGROUND OF THE INVENTION AND PRIOR ART
In DC-DC power supply of different kinds of electrical devices, power rectifiers are utilized m order to output a correct rectified output voltage. Typically a diode would be employed on the secondary side m order to obtain the rectified output voltage .
One way of obtaining a suitable rectifier circuit is to use flyback topology. In a flyback topology a primary side stores magnetic energy m a magnetisable core or the like during a charging interval. The energy is then fed to a secondary side during the so called flyback interval. The main advantage of a power rectifier circuit having a flyback topology compared to other rectifier circuits is its simple construction, which makes it cheap to manufacture.
Furthermore, flyback converters can be divided into two different kinds:
- continuous mode flyback converters, and
- discontinuous moαe flyback converters.
In a continuous mode flyback converter the magnetic energy never drops to zero so that energy is continuously flowing either m or out of the core of the transformer, whereas m a discontinuous mode, intervals when energy is neither flowing m nor out of the core of the transformer occurs.
However, m a conventional flyback converter as seen m Fig. 1, which comprises, on the primary side, a primary winding 101 of a transformer 105 and a switch 103, and on the secondary side a secondary winding 107 of the transformer 105 connected to a diode 109 and an output capacitor 111 over which a load 113 can be connected, there is a problem associated with the voltage 2
drop over the diode 109. Thus, in the case when the output voltage over the output capacitor 111 is low, e.g. less than 5 V, the voltage drop over the diode 109 becomes a significant part of the overall voltage, which makes the power converter inefficient for such low voltage applications.
Furthermore, US patent No. 5,237,606 describes a power converter to be located in a remote terminal of a telephone system. The power converter is designed to be able to operate both in a continuous mode and in a discontinuous mode, which can occur in the specific application for which the power converter is designed. The power converter deals with the problem of a large voltage drop over the rectifying diode on the secondary side by means of using a FET transistor. However, since the aim is to provide a power converter which can operate both in a continuous mode and in a discontinuous mode, the circuit is not well suited for use in a continuous mode. This is due to the fact that in order to work properly in the discontinuous mode, control circuits are required, which besides being expensive, also galvanically interconnects the primary and secondary side of the power converter, thereby taking away the galvanic isolation between the primary and secondary side.
SUMMARY
It is an object of the present invention to overcome the problems as outlined above and to provide a continuous mode flyback converter which has a simple construction, and yet being efficient compared to the converters according to the prior art.
This object and others are obtained by the power converters as set out in the appended claims .
Thus, by replacing the diode as conventionally used as a secondary switch in the secondary side of the DC-DC converter by a FET transistor a much lower voltage drop is achieved, which thus reduces the losses on the secondary side. The FET transistor is then directly connected to an auxiliary winding arranged in series with the secondary winding of the transformer. 3
Furthermore, by introducing a DC-blockmg capacitor m a control arrangement on the secondary side the voltage provided by the auxiliary winding can be significantly reduced, thus reducing the driving losses.
Also, if a short-circuit of the output of the converter should occur sufficient voltage will still be available for turning the secondary switch on and off .
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described m more detail by way of non- limiting examples and with reference to the accompanying drawings, m which:
- Fig. 1 is a circuit diagram of a continuous mode DC-DC converter according to the prior art.
- Fig. 2 is a circuit diagram of a continuous mode DC-DC converter having a FET transistor as rectifying component.
- Fig. 3 is a circuit diagram of a continuous mode DC-DC converter having a FET transistor as rectifying component and having an improved drive circuitry.
DESCRIPTION OF PREFERRED EMBODIMENTS
In Fig. 2 a DC-DC converter is shown. The power converter comprises on the primary side a primary winding 101 and a switch 103, the primary winding being supplied with power from a DC voltage source 102. The DC-voltage source can m turn be connected to an AC-voltage supply (not shown) via a rectifying circuit. The primary side feeds a secondary side with energy via a transformer 105. The secondary side comprises a secondary winding 107 and an auxiliary winding 108 connected m series with the secondary winding 107. A FET transistor 110 is with its source terminal connected to a point between the secondary winding 107 and the auxiliary winding 108. The gate of the transistor 110 is directly connected to the other end of the auxiliary winding 108 and the dram of the transistor 110 is connected to one end of an output capacitor 111. The other end of the output capacitor is connected to the free end of the secondary winding 107. A load 113 can then be applied over the output capacitor 111, thus connected m parallel thereto.
SIJBΓTITUTE SHEET (RULE 26) 4
When the switch 103 is closed current flows through the primary winding 101, due to the voltage applied over it from the voltage source 102. The current flow through the primary winding 101 will store energy into the magnetic core of the transformer 105. When the switch 103 is turned off, the polarity across the secondary winding 107 will change and a current caused be the energy stored in the magnetic core is fed through the transistor 110 to the output terminal over the capacitor 111. This is possible thanks to the arrangement with the auxiliary winding 108, which will provide a voltage at the gate of the transistor 110 when the switch 103 is in an open state, since the auxiliary winding has the same polarisation as the secondary winding 107. Hereby a control pulse is fed to the transistor 110 so that the channel of the FET transistor will be conducting when the switch 103 is in an open state.
The advantage of such an arrangement compared to the arrangement described above in conjunction with Fig. 1, is that the voltage drop over the diode 109 is replaced by the voltage drop over the FET transistor, which typically is much smaller. I.e. instead of a voltage drop of 0.3 - 0.7 V, which is common for most diodes a voltage drop of less than 0.1 V can be obtained, whereby the efficiency of the DC-DC flyback converter is increased, especially when the output voltage is small, e.g. less than about 5 V. Furthermore, as is obvious, the smaller the output voltage the more important the use of a rectifying component having a low voltage drop becomes .
However, by using the arrangement in Fig. 2 instead of the arrangement in Fig. 1, driving losses are introduced, since the mean value of the voltage across the auxiliary winding 108 is zero, and thus large negative amplitudes will be applied to the gate of the transistor 110 as a result of a sufficiently high gate drive voltage. Furthermore, if the output terminals of the converter is shortened, the voltage from the auxiliary winding will drop far below the gate threshold value of the transistor 110, which will cause the output current to flow via the body drain diode of the FET transistor 110, which, in turn, will significantly increase the power dissipation. This problem can however be overcome by the arrangement as shown m Fig. 3. Thus, m order to reduce driving losses, a DC- blockmg capacitor 117 is inserted between the output terminal of the auxiliary winding 108 and the base of a PNP transistor 115 arranged connection to the transistor 110. Due to the collector-base diode the transistor 115, the gate voltage of the FET transistor 110 is prevented from going negative. The transistor 115 also provides a very quick turn off of the channel the FET transistor 110, so that the switch loss will be reduced to a minimum.
The base of the PNP transistor 115 is through the blocking capacitor 117 connected to the free output terminal of the auxiliary winding 108, the emitter of the PNP transistor 115 is connected to the gate of the FET transistor 110 and the collector of the PNP transistor 115 is connected to the source of the FET transistor 110.
In a preferred embodiment the base and the emitter of the PNP transistor are interconnected by a resistor 119 for providing a voltage drop between the base and the emitter of the transistor 115. The resistor can be replaced by a diode or another component, which can provide the voltage drop.
Finally, as stated above, by locating the DC-blockmg capacitor 117 m the drive arrangement, control pulses will be fed to the gate of the FET transistor 110 even m the event that the output terminals of the DC-DC power converter should be shortened. This is very advantageous since if no control pulses would be fed to the FET transistor 110 the output current should be forced to go through the body diode of the FET transistor 110. This would lead to high losses and possibly the FET transistor could be damaged .
The topology as described above can also be applied to other types of converters, such as Cuk and SEPIC converters.
SUBSTITUTE CHfXT (PVJLE 28)

Claims

1. A continuous mode flyback converter having a primary and a secondary side, the secondary side comprising a secondary winding (107), characterized in that the secondary side also comprises an auxiliary winding (108), a first terminal of which is directly connected to the gate of a FET transistor (110) and the other, second, terminal of which is directly connected to the source of the FET transistor (110) .
2. A converter according to claim 1, characterized in that the secondary side further comprises a PNP transistor (115), the emitter of which is connected to the gate of the FET transistor (110) , the collector of which is connected to the source of the FET transistor, and the base of which is connected to the first terminal of the auxiliary winding.
3. A converter according to claim 2, characterized in that a resistor (119) or diode is connected between the base and emitter of the PNP transistor (115) .
4. A converter according to claim 3, characterized in that a capacitor (117) is interconnected between the first terminal of the auxiliary winding (108) and a point on the path interconnecting the gate of the FET transistor (110) and a terminal of the resistor or diode.
5. A continuous mode flyback converter having a primary and a secondary side, the secondary side comprising a secondary winding (107), the secondary side also comprising an auxiliary winding (108) connected to the gate of a FET transistor (110), characterized by a DC-blocking capacitor (117) interconnected between the auxiliary winding (108) and the gate of the FET transistor (110) .
6. A converter according to any of claims 1 - 5, characterized in that the converter is a Cuk or SEPIC converter instead of a flyback converter.
EP99948572A 1998-05-07 1999-05-07 A continuous mode flyback converter Withdrawn EP1092261A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE9801595 1998-05-07
SE9801595A SE514850C2 (en) 1998-05-07 1998-05-07 Synchronous rectifier in flyback topology
PCT/SE1999/000770 WO1999057799A1 (en) 1998-05-07 1999-05-07 A continuous mode flyback converter

Publications (1)

Publication Number Publication Date
EP1092261A1 true EP1092261A1 (en) 2001-04-18

Family

ID=20411217

Family Applications (1)

Application Number Title Priority Date Filing Date
EP99948572A Withdrawn EP1092261A1 (en) 1998-05-07 1999-05-07 A continuous mode flyback converter

Country Status (7)

Country Link
US (1) US6424544B1 (en)
EP (1) EP1092261A1 (en)
CN (1) CN1299529A (en)
BR (1) BR9910277A (en)
SE (1) SE514850C2 (en)
TW (1) TW563288B (en)
WO (1) WO1999057799A1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6839248B2 (en) * 2003-05-01 2005-01-04 Ko Semiconductors Co., Ltd. Flyback power supply device and control method thereof
US6856149B2 (en) * 2003-06-19 2005-02-15 Niko Semiconductor Co., Ltd. Current detecting circuit AC/DC flyback switching power supply
DE10339470A1 (en) * 2003-08-27 2005-03-31 Friwo Mobile Power Gmbh Control circuit for a switching power supply
TWM255583U (en) * 2004-04-05 2005-01-11 Power Mate Technology Co Ltd Flyback type conversion circuit
US7907426B2 (en) * 2008-08-11 2011-03-15 Fsp Technology Inc. Flyback circuit providing synchronized control
TWI497892B (en) * 2012-07-13 2015-08-21 Tpv Electronics Fujian Co Ltd Liquid crystal display products and its flyback power conversion device
AT14080U1 (en) * 2013-08-12 2015-04-15 Tridonic Gmbh & Co Kg Control circuit for a control gear for bulbs
DE102013219015A1 (en) * 2013-09-20 2015-03-26 Osram Gmbh Synchronous rectifier
US9819271B2 (en) * 2013-09-30 2017-11-14 O2Micro, Inc. Power converters
CN110391732A (en) * 2019-07-31 2019-10-29 青岛大学 A kind of Bootstrap formula SEPIC converter based on synchronous rectification
CN111049391A (en) * 2019-12-24 2020-04-21 普联国际有限公司 Off-line flyback converter and power supply equipment

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06339266A (en) * 1993-05-26 1994-12-06 Nec Corp Flyback converter using mos transistor as synchronous rectifier

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US4716514A (en) * 1984-12-13 1987-12-29 Unitrode Corporation Synchronous power rectifier
US4677536A (en) * 1986-03-17 1987-06-30 Tektronix, Inc. AC Current sensing circuit
JPH0734653B2 (en) * 1989-09-05 1995-04-12 九州大学長 Power supply
JP2682202B2 (en) * 1990-06-08 1997-11-26 日本電気株式会社 Rectifier circuit using field effect transistor
JP2819932B2 (en) * 1992-03-05 1998-11-05 日本電気株式会社 MOSFET rectifier circuit of forward converter
US5303138A (en) * 1993-04-29 1994-04-12 At&T Bell Laboratories Low loss synchronous rectifier for application to clamped-mode power converters
JP2795217B2 (en) * 1995-06-01 1998-09-10 日本電気株式会社 Synchronous rectification type converter
JP3505068B2 (en) * 1997-10-24 2004-03-08 富士通株式会社 Synchronous rectification DC-DC converter

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Publication number Priority date Publication date Assignee Title
JPH06339266A (en) * 1993-05-26 1994-12-06 Nec Corp Flyback converter using mos transistor as synchronous rectifier

Also Published As

Publication number Publication date
WO1999057799A1 (en) 1999-11-11
US6424544B1 (en) 2002-07-23
SE9801595L (en) 1999-11-08
SE9801595D0 (en) 1998-05-07
SE514850C2 (en) 2001-04-30
BR9910277A (en) 2001-01-02
CN1299529A (en) 2001-06-13
TW563288B (en) 2003-11-21

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